Turbomachines, for example steam or gas turbines, compressors or the like, have components particularly in their flow channel which are exposed to high physical and chemical stresses during operation of the turbomachine. Such components are particularly guide vanes and rotor blades, but also wall elements which form the flow channel or clad it. Particularly in gas turbines, the components exposed to hot gas experience a multiplicity of effects during normal operation, the instance due to corrosive media, an oxidizing atmosphere, high temperatures or foreign bodies. This can cause the components to become damaged or suffer ageing.
For stringent requirements of the components, for example those in gas turbines, it is intended that these components should be made of composite ceramic materials which, for example, may be formed by a composite of ceramic and metal, or different ceramic materials. In order to be able to meet the stringent requirements during operation of the turbomachine and in order to be able to achieve a high efficiency, components made of composite ceramic materials, particularly combinations of different ceramic materials, are increasingly used more and more in the prior art. In order to improve the typically brittle fracture behavior, one ceramic material i.e. the matrix material is inlaid with a further material having a different structure than the matrix. An increased resistance to external effects can be achieved i.e. small faults in the material, for example generated during production or by stress in operation, do not lead directly to damage of the components. In order to improve the properties of the composite materials, it is known to provide particle reinforcement, for example whisker reinforcement. In such ceramics, however, it is necessary to ensure that the short fibers i.e. whiskers remain bound in the ceramic matrix during normal operation, since these are assigned to a high hazard class because they can enter the lungs. Preferably long fibers have therefore been used to date, which are made of glass or glass ceramic comprising e.g. SiC, Al2O3, C, BN or Si3N4 or a combination of these. If damage to such a component then occurs, it has previously been customary to turn off the turbomachine and replace the damaged component. Otherwise, it is to be feared that the damaged component may cause further worse damage to the turbomachine which can entail enormous repair outlay and a long downtime.
The replacement of a defective component may lead to a long downtime, particularly if the component is not available from store. A further undesirable effect of replacement is that the components of the turbomachine will have different ageing states. During later routine maintenance, components that could still withstand a subsequent operating cycle might then be replaced.
US 2003/0196305 A1 discloses a method for repairing ceramic composites, in which the site to be repaired is filled layer-wise with fiber-reinforced bands. There are consequently no fiber junctions between the individual bands, so that the bands have a poor mechanical bond between them.
Further prior art is known from US 2002/018236 A1, EP 1 251 191 A1, U.S. Pat. No. 5,444,911 and EP 1 063 210A1.